There has been a rapid increase in recent years, in demands for a gallium nitride compound semiconductor to be used as a device for a light emitting diode, laser diode, and the like concentrated in the field of illumination. There is known, for instance, as a process for manufacturing a gallium nitride compound semiconductor, a metal-organic chemical vapor deposition (which may be abbreviated as MOCVD below) process in which a semi-conductor film of a gallium nitride compound is subjected to chemical vapor deposition on a substrate of sapphire or the like which has been set in advance in a reactor chamber so as to form an objective film by using, as a group III metal source, an organometallic gas such as trimethylgallium, trimethylindium and trimethylaluminum and by using ammonia as a nitrogen source.
In addition, there is available, as an apparatus for manufacturing the above-mentioned gallium nitride compound semiconductor, a horizontal or a vertical chemical vapor deposition apparatus comprising a horizontal susceptor for mounting a substrate thereon, a heater for heating the substrate, a feed gas introduction portion, a reaction gas exhaust portion, and a rotary axis for supporting the susceptor. The horizontal or the vertical chemical vapor deposition apparatus is of such constitution that the substrate is mounted on the susceptor, the substrate is heated, and thereafter two kinds or more of gases containing a feed gas is supplied in a reactor in the direction parallel or vertical to the substrate so that a semiconductor film is subjected to chemical vapor deposition to form a film on the substrate.
In a process for manufacturing a gallium nitride compound semiconductor, heat resistance and corrosion resistance are required not only for the substrate or the susceptor that will be heated to an elevated temperature but also for the heater itself because the substrate is heated up to 1000° C. or higher together with supplying the corrosive feed gas onto the surface of the substrate. Conventionally, various heaters applicable under an atmospheric corrosive gas with an elevated temperature or a chemical vapor deposition apparatus employing the same have been developed. For example, Japanese Unexamined Patent Application Laid-Open No. Hei 5-206100 discloses an apparatus for manufacturing semiconductors equipped with a heater protected by a quartz tube. Japanese Unexamined Patent Application Laid-Open No. Hei 8-17745 discloses a heater covered by high purity thermally decomposable graphite and a heater covered by silicon carbide. Japanese Unexamined Patent Application Laid-Open No. Hei 11-233244 discloses a hot plate for the CVD apparatus wherein the hot plate comprises three layers of aluminum plate layer having a heater on one surface and reinforcing materials on the other surface. Further, Japanese Patent Laid-Open No. 2003-133225 discloses a heater formed on one surface or inside of a plane plate made of nitride ceramic or carbide ceramic.
However, even the above heater covered with the heat-resistant material or the corrosion-resistant material had a disadvantage of decreasing the effect of covering with the heat-resistant material or the corrosion-resistant material because a difference of a coefficient of thermal expansion between the heat source and the heat-resistant material or the corrosion-resistant material causes deformation and crack of the heater after a repeated use from a room temperature up to a temperature of 1,100 to 1,200° C. Furthermore, in addition to such a situation, because a tough use of the materials under an ambient atmosphere at the temperature of 1,100 to 1,200° C. and 10 to 50% by volume of ammonia gas degrades the materials and breaks the heater in relatively short period, it was necessary to frequently renew the heater.
Additionally, by disposing a quartz plate which transmits heat ray radiated from the heater and which is separated from the heater with a space, it is conceivable to shield the corrosive gas from the heater. However, the quartz plate suffers plastic deformation under the above elevated temperature, and the plastic deformation gradually enlarges with repetitions of heating and cooling, and as a result, for example, the quartz plate hangs down and touches with other component in a reactor chamber. Because it induces a problem of damaging the chemical vapor deposition apparatus, renewing the quarts plate in relatively short period was necessary. Especially in a large-scale apparatus capable of chemical vapor depositing plural of the substrate simultaneously, the problem of plastic deformation of quartz had a tendency of becoming serious because a quartz plate with large size corresponding the scale of the apparatus was necessarily employed.